The invention relates to a navigation device and a position correction method when traveling in non-digitized areas by means of dead-reckoning navigation.
A device of this type is used, in particular, in motor vehicles. Navigation devices have a sensor arrangement for determining a distance and a direction. A tachometer signal or an odometer signal is normally used to determine distance and a gyroscope to determine direction. In addition, GPS (Global Positioning System) location can be used. The values determined by the sensor arrangement are converted by means of a processor into a position. This position is then normally compared with a road map digitized on a storage medium. The driver of the motor vehicle is finally informed of the current position by means of a display, e.g. a color LCD display.
The digitized road map normally includes all roads which are accessible to the public. Private installations, e.g. factory sites or leisure installations, and also multi-story car parks, off-road areas with their roads and paths and the like are not normally recorded on these digitized road maps. If the motor vehicle is travelling in non-digitized areas of this type, the sensor system of a navigation system cannot be matched with the paths which are to be traveled. Sensor drift, in particular at system start-up, causes substantial deviations of the vehicle alignment and position. If a vehicle is located in an off-road area or an outdoor, unrecorded area, the current position can be determined by means of satellite location (e.g. GPS) and/or location via cellular networks (GSM, UMTS), and can be synchronized on re-entering the digitized road network. However, the sensor system often cannot be synchronized by these auxiliary means, since a function of this type is often not guaranteed, particularly in multi-story car parks.
The object of the present invention is therefore to indicate a method and a device for position correction in a navigation system for traveling in non-digitized areas by means of dead-reckoning navigation. This object can be achieved by a method for position correction in a navigation system when traveling in non-digitized areas by means of dead-reckoning navigation, comprising the following steps:
detection of travel in a non-digitized area;
determination of at least one principle axis direction;
comparison of the direction of travel with the previously defined principle axis direction; and,
in the event of matching within a predefined limit, correction of the direction of travel according to the principle axis direction.
A principle axis direction can be detected by means of a straight-line journey of predefined length. A principle axis direction can be defined by means of a journey within a predefined window area. The determined principle axis directions can be allocated to the non-digitized area and stored. At least one entry road of predefined length into the non-digitized area can be stored with reference to the non-digitized area. At least one exit road of predefined length from the non-digitized area can be stored with reference to the non-digitized area. The position detection can be de-activated until the previously stored exit road is detected after detection of a previously stored entry road. After detection of a previously stored reference point, the position detection can be de-activated until the previously stored exit road is detected.
An exemplary embodiment of a navigation device for dead-reckoning navigation according to the present invention, may comprise:
at least one sensor arrangement for determining a distance and a direction,
at least one processor for position calculation based on measured values of the sensor arrangement, which is connected to a memory,
a digitized road map stored on a storage medium with digitized areas, with which a calculated position is compared, wherein
the processor, on entry into a non-digitized area, determines at least one principle axis direction and stores it in the memory, and
the processor compares the current direction of travel with the previously determined principle axis direction and, if necessary, corrects it according to the principle axis direction.
The processor may detect a principle axis direction by means of a straight-line journey of predefined length. The processor may define a principle axis direction by means of a journey within a predefined window area. The processor can allocate the determined principle axis directions to the non-digitized area and stores them. The processor can store at least one entry road of predefined length into the non-digitized area with reference to the non-digitized area. The processor may store at least one exit road of predefined length from the non-digitized area with reference to the non-digitized area. After detection of a previously stored entry road, the processor can deactivate the position detection until the previously stored exit road is detected. After detection of a stored reference position, the processor may de-activate the position detection until the previously stored exit road is detected.
The present invention makes use of the attribute pertaining to the existence of xe2x80x9cpreferred directionsxe2x80x9d, in particular, inside multi-story car parks. These preferred directions are not limited to a plane or to an orientation. Preferred directions are, in particular, longer entry and exit paths. The inventive method detects a departure from the digitized area and then determines a preferred direction that is defined as a principle axis or a principle axis direction. When traveling within the non-digitized area, e.g. of a multi-story car park, the system monitors whether the vehicle moves within a predetermined limit of the previously defined principle axis direction. If this is the case, it is determined whether a deviation exists and this deviation is optionally corrected to conform with the principle axis direction. This enables compensation of errors that are caused, in particular, by the direction detection.
In a further development, the system can record and store entry and exit roads of a non-digitized area. On entry into a non-digitized area, a specific, definable length of an entry road can be allocated to the non-digitized area and stored in the memory. The system then operates using the method described above. As soon as the system detects that the non-digitized area has been left, a predefined length of the last-traveled road can be stored as an exit road. If the vehicle is subsequently to travel in the same non-digitized area, this can be detected through comparison with the previously stored entry road and the position determination can be deactivated. The system then waits until the previously stored exit path is detected and reactivates the position determination.
In a further development, the digitized road map can be extended to include the newly-traveled paths. These newly-recorded paths are stored in a similar manner to the road network which is already permanently stored.